It seems to be based on the information gathered by Geoffrey Jaggard. Jaggard had hoped to publish such a concordance but could not find a publisher interested and ended up using some of the matter in "wooster's World" and "Blandings The Best" (which are interesting and amusing!)

I was considering buying the Concordance but I have never even seen a copy. It runs to 8 volumes and I'm a bit wary of spending that much money on something that I don't really know anything about.